Extraction of tar and tar constituents from gases.



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UNITED STATES PATEN ormoa.

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Specification or letters Patent. Patented J uly 19 1910, Applicationfiled Kay 7, 1910.- Serial No. 580,058 v a v To all whom it may concern:

. Be it knownthat I, WALTHER FELD, a subect of the Kin of Prussia andthe German of onningen-on-the-Rhine, in the Kingdom of Prussia andGerman Empire, have invented new and useful Improvements in theExtraction of Tar and Tar T Constituents from Gases, of which thefolcentigrade, and that these gases come from lowing is a specification.

Recently the extraction of tar from gases has been efiected by means ofhot tar before the gases are cooled to atmospheric temperature. Thisprocess, as described in the s ec'ification of Letters Patent No.951,778

D. 1910 granted to me, offers no difficulty with gases, the temperatureof which is kept above tho dew point of water, and in using tar, or taroils, free of water, as a washing liquid. In many cases, however, inwhich tar, or tar constituents, are to be extracted from gases, .thegases are saturated with water, and in such cases, tar, or tarconstituents, mixed with water, will be separated and the washingeffecLwill be considerably affected. The simultaneous separation ofwater and tar prevents the fine tarry mist from combining to form drops.In such cases, means must be provided to avoid the simultaneousseparation of water and tar.

According to my aforesaid Patent 951,778 A. D. 1910 the separation of anundesired constituent is generally avoided by raising the gases abovethe dew point of the undesired constituent, or by lowering the dew pointof the undesired constituent by adding extraneous gases, or vapors.

In order to separate tar, or tar constituents, from water-saturatedgases I, accordin to my present invention, proceed as to lows. Thewater-saturated gases are, before entering the tar-washer, superheatedand then treated with the washing liquid, which is also heated to thesame, or to a higher, temperature. I proceed in the same way inextracting tar constituents, for instance naphthalene, :from gases.

The following is a description of an example of the process according tomy present invention, presuming that coal gas is to be treated. at anelevated temperature for the extraction of tar, and afterwardnaphthalene is to be separated. Supposing the dew point of these gasesfor water to be 70 centigrade, and for naphthalene 30 the mains andcoolers saturated with water (that is to say at 70 centi ade), 0.considwashers, superheated to such an extent as is necessary toevaporate the water fog. Although superheating from 70 to 72 centigradewould be su'flicient, it is better to superheat to, or above, 80centigrade. The superheating may be performed by any external, orinternal, supply of heat, for instance by pipes heated by steam, or bythe hot gases themselves, coming from the ovens, or retorts, or by wastegases, or the like, using the principal of counter-current; or ifsuperheated gases, or vapors, (for instance superheated steam) beintroduced into the gases. It will also answer the purpose if thewashing liquid be correspondingly heated and the gases'be treated withsuch a quantlty thereof that the necessary heat is supplied to the gasesin the washing process. The amount of heat necessary for thesuperheating of the water-saturated gases, for instance from 70, to 80,centigrade, results from the following calculation. The watersaturatedgases at 7 0 centigrade have a heat capacity of 0.5 calories per cubicmeter (calculated at 0 centigrade and in a dry state). In order tosuperheat the gases from 70 to 80 centigrade, ficalories are necessary.The

specific heat of tar (free of Water) is also 0.5 calories. In order totreat the gases of" 70 centigrade at 80 centigrade with one 1 liter oftar of 80 centigrade, this tar must be heated to about 90 centigrade andthen .be intimately treated with the gases of 70 centigrade. ;will beheated from 70 to 80 oentigrade L and the tar be cooled from 90 to 80centi- 7 grade.

By this treatment, the gases If more than one liter of tar be used forone cubic meter of gas, the tar may be correspondingly less heated; ifless tar be used, it must be heated to a correspondingly higher degree.In case the gases enter the tar washer water-saturated, they contain, as

hereinbefore explained, finely divided water fogs, which must beevaporated. In this erable portion of tar, toget er with a small willtar wil case the supply of heat and the heating ofthe ar must beincreased accordingly. This also necessary if the tar, used for thetreatment of the gases, containwater. In this case the tar, or thegases, on-both, is, or are, heated to-an extent necessary to evaporatethe water from the washing tar. As long as the gases contain'water fogs,or the tar contains water, the extraction of tar is incomplete. Byusing, over and over again, for the washing process, the tar runningfrom the washing apparatus, and by removing only the excess of'such tar,the Washing become free of water after some time. Instead of tar, taroils, or the like, may be used, the process being always the same. Forthis purpose any suitable appa ratus may be used which will allowintimate treatment of the gases with the washing liquid. A convenientapparatus is such as is described in the specification of my Patent No.829,261 A. D. 1906. Or exhaust apparatus, or fans, by which the washingliquid is injected, or centrifugal apparatus of any suitable kind, orinjectors, or spraying apparatus, and the like, may be used for thepurpose. In order that the last traces of tar may be extracted from thegases, a so-called Pelouze apparatus may be employed in combination withthe gas washer. Means should be provided to insure that the gases arenot cooled to the dew point for water if they pass this apparatus, and,forthis purpose, it is convenient to have the apparatus and pipeconnections, by which the gases pass in the washing process, protectedagainst cooling effects by insulation, or to have the gases so farsuperheated that they are not cooled to the dew point of watersaturation while they are passing the tar extractors.

After the aforesaid treatment, the gases will be free of tar at 70centigrade, but

7 they will be saturated with bar oils of high boiling points accordingto their quantity and point of evaporation. It will be the same withgases the dew point of which is above, or below, 70 centigrade.

After the extraction of tar, the gases may be conveniently treated forthe extraction of cyanogen and ammonia. In order that in theseoperations no tar oils shall be se arated, the gases should be againraised according to the aforesaid Patent 951,778 A. D. 1910) above thedew point of the tar oils left in the gases. As the washing liquids aresuch as contain water, the gases, which were superheated in the tarextraction, will again be saturated with water.

The dew point of the gases for tar oils should therefore be lowered byadding gases, or by injecting vapors, which maybe done according toBritish Patents Nos. 27,567 and 28,390 A. D. 1907. The extraction ofammonia. may be conveniently performed by acids, or by salt solutions,eventually simultaneously with the cyanogen, for instance according tothe Patent 806,467 A. D. 1905, or by any other suitable process, atcentigrade, or above. After adding gases which contain only a' smallquantity of tar oils, the extraction of ammonia may, if desired, beperformed at a lower temperature than 70 centiigrade without tar oilsbeing separated. A er the gases have thus been freed from tar, cyanogen,and ammonia, they must be cooled. In cooling below 70 centigrade, taroils will be separated according to the Patent 951,778 A. D.

1910, but the'amount of these tar oils is but small in coal gases.

' As the dew point of the gases for naphthalene lies at about 30centigrade, there is the danger that the small amount of tar oils,separated when the gases are cooled from 70to 30 centigrade, will not besufiioient to dissolve the naphthalene deposited at 30 centigrade. Incooling, water will be separated, as well as tar oils, according to thelowering of the tension of water vapors from 70 to 30 centigrade, andtherefore the tar oils separated will contain water, whereby theirwashing and dissolving efficiency will be affected. If this be the case,the gases are, in the first instance, only cooled to 30 centigrade, andthen they are, according to this invention, treated with a washingmedium for the extraction of naphthalene. Also the treatmenthereinbefore described for the extraction of tar is effected in such away that the gases, which are water-saturated at 30 centigrade, aresuperheated and then treated with the washing liquid, in order toprevent the separation of water and the reduction of the washingefiiciency. The operation is the same as hereinbefore described for thetar extraction. In this present case, superheating of the gases from 33to 36 centi rade will be sufiicient, although it may be higher, but thenthe dissolving power of the washing liquid for naphthalene will bediminished. Any solvent for naphthalene may be used as a washing liquid,but it is preferable to use, for this purpose, high boilin tar oils, ortar, which may be those obtaine by the previous treatment of the gases.After the extraction of naphthalene is performed, the gases may becooled to the desired temperature without any danger of obstruction bynaphthalene. The small amount of naphthalene which mi ht be depositedwill be dissolved by tar 011s and be condensed simultaneously. Insteadof the separated extraction of tar and naphthalene, both these may beextracted simultaneously by first cooling the gases to the dew point ofnaphthalene and then treating them according to the process described,

If, in the rocess for extracting tar, tar oils, or tar, be usedcontaining much meand if the washin oints, liquid be strong y eatedbefore entering t e gas washers, a corresponding amount of vapors ofthesaid oils will be incorporated with the gases. In this case, whenafterward cooling the gases, the said oils will be separatedsimultaneously with the naphthalene, which will therefore be dissolved,and consequently special treatment of the, gases for the extraction ofnaphthalene will not be necessary. I

Instead of extractin cyanogen and armmonia from the gases a ter theextraction of tar, these operations may be performed after theextraction of naphthalene, for example by dissolving the ammonia byacid, or by a salt solution, or by water. In this latter case, it isconvenient to reintroduce the ammonia obtained in the form of weakammonia liquors, into the warm ases according to Patent No. 830,983 A.1906. If then the gases be cooled in a separatesurface cooler, forinstance from 55, or to 30, or 20, centigrade, strong ammonia liquorswill be obtained, which, according to the conditions and to the amountof ammonia in the gases, may beraised to from 7 to 10 per cent. If, forinstance, the crude gases contain 8 grams of ammonia per cubic meter, ofwhich 2 grams ma be condensed with the water separated be ore, andafter, the tar-extraction, in coolin down to about centigrade, and ofw-hlch a further 2 grams may be dissolved by water after the naphthaleneextraction, and if the/ammonia of these weak 1i uors thus obtainedbeintroduced by distil ation into the gases before they are cooled to,or under, 55 centigrade, the gases will be of a temperature of bedium,or light, oils of low boilin tween 55 and 30 ing 111 and while theextraction of centigrade and 8 grams of ammonia will be deposited. As,at from 55 to 30 centigrade, 112 grams of water will be separatedsimultaneously, this water will contain about 7.8 per cent. of ammonia.After further cooling, for instance from 30, to 20 centigrade, theremaining 2 grams of ammonia w1ll be extracted by water and these 2grams will, as aforesaid, be reintroduced into the gases.

I claim- 1. In the aforesaid process of extracting tar and tarconstituents from gases containing water; superheating the gases abovetheir dew and while, the extraction of tar and tar constituents isperformed.

2. In the aforesaid process of tar and tar constituents from asescontainwater; the employment 0 washing liqheated to a temperaturesufficient to keep the gases under treatment above their dew oint ofwater saturation.

3. in the aforesaid process of extracting tar and tar constituents fromgases contain-.

ing water; superheating the gases above their dew point of watersaturation, before tar and tar constituents'is performed, cooling saidgases, again superheatingthe gases, and treating the same with a washingliquid for the extraction of naphthalene.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

- 'WALTHER FELD. Witnesses:

LoUIs VANDORN,

point of water saturation, before,

extracting

